There are a number of mining operations worldwide that produce minerals by the processing of clay and sand bearing ores. Examples of such operations are oil sands extraction, phosphate rock mining, china clay mining, diamond mining and bauxite refining.
Waste products from such processes are inorganic materials such as sand and clays and process waters contaminated with suspended organic and inorganic matter. The process waters often contain dissolved organic and inorganic matter as well. The simplest method of disposal of such byproducts would be to return them to mined-out areas. This disposition is acceptable for rapidly settling, coarse, compactable components such as sand. Generally the mined-out areas will accommodate only the settled sand. However, the clays are generally of the swelling variety and form slimes at 5-10 percent solids concentration along with dispersed organic matter. These slimes increase the volume of total wastes to be disposed of by 30 to 40 percent.
A common practice has been to impound the slimes in ponds formed by building dikes with the sand fractions. With settling times of weeks, months or years the solids content at mid-depth of ponds may reach 20-30 percent and the surface layer may reach sufficient clarity to be recycled. It is possible to reach a steady state at which the recycled water volume suffices for mining or other operations and the pond area does not expand. However, in such practice the ponds require enormous areas. Furthermore, organic matter which accumulates on the pond surfaces creates an environmentally unacceptable situation.
The clay slimes problem as related to heavy oil (bitumen) recovery from tar sands has been described by many; for example, Frederick W. Camp, "Processing Athabasca Tar Sands--Tailings Disposal", The Canadian Journal of Chemical Engineering, Vol. 55, October, 1977, pages 581-591. A general review is given by M. A. Kessick, "Clay Slimes from the Extraction of Alberta Oil Sands, Florida Phosphate Matrix and Other Mined Deposits", Canadian Mining and Metallurgical Bulletin, February 1978.
The critical need is to find means to reduce tailings volume, greatly increase the fine particle settling rate to provide more efficient water recycle, and eliminate insoluble and soluble organic matter from ponded water. The review lists many methods which have been studied; none has satisfactorily met the needs. Included in these methods are addition of flocculating agents, pH reduction, bacterial treatments, ultrasonics, agglomeration, electrophoretic methods, freeze-thawing and co-filtration with fly ash.
Slimes resulting from mining and processing of clay and sand bearing ores are typically very difficult to consolidate and dewater. This invention is a method for treating such slimes whereby the land area required for final disposal is greatly reduced and water removed from the slime may be re-used in the mining or processing operations.
The wet oxidation procedure, used in the process of the instant invention, is a well developed, commercially used technique and is described, for example, in Pradt U.S. Pat. No. 4,100,730 (Jul. 18, 1978), Gitchel et al. U.S. Pat. No. 3,359,200 (Dec. 19, 1967), Zimmermann U.S. Pat. No. 2,824,058 (Feb. 18, 1958) and Hoffman U.S. Pat. No. 3,876,497 (Apr. 8, 1975). Although the process has been used in many different ways there is no reference in published literature to application in treating clay slimes or any medium of "swelling type".